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Apparent Pneumonia Outbreak in Colorado Sheep

Colorado Division of Wildlife officials are working to determine what caused at least eight bighorn sheep to die east of Gunnison during the last week of December.

A rancher called the DOW's Gunnison office on December 23 and reported that three bighorns were dead near one of his fields. A small herd of wild sheep winters on a hillside just above the pasture and often move down to feed on hay left for cattle. DOW wildlife officers examined the carcasses and collected tissue samples. Another bighorn in the pasture that appeared to be very sick was euthanized.

Wildlife officers found four more dead sheep during the next three days.

Initial findings from postmortem examinations done in the field suggested that pneumonia was the likely cause of at least some of the bighorn deaths. Other carcasses were found frozen and were transported to the DOW's Wildlife Health Laboratory in Fort Collins for complete necropsies and testing to determine cause of death. Upon examination in the laboratory all eight dead bighorns showed some evidence of pneumonia. Results from additional lab work will probably be available by mid-January.

J Wenum, area wildlife manager in Gunnison, said bighorns are very susceptible to pneumonia.

This band of wintering sheep is part of the Fossil Ridge herd, which is estimated to be approximately 50 animals. The death of eight bighorns is significant for such a small population. DOW officials are keeping a close eye on the remaining animals and evaluating management options. Unfortunately, delivering antibiotics to wild bighorns is problematic and past attempts to treat pneumonia outbreaks in bighorns around the state have not been particularly successful.

"It's not like cattle where you can run them into a pen and make sure they get the proper dose," Wenum said.

Treatment options available to wildlife managers are limited. Antibiotics may be combined with feed, but there is no way to assure that all of the target animals are properly treated. Some antibiotics can be injected using darts fired from rifles, but it is difficult to ensure that all animals receive treatment and that they receive the proper dosage. Bighorns also can be trapped and treated, but that is risky in a population that is ill and physically stressed.

"It's very labor intensive and there is no guarantee that these treatments help the animals, but we are evaluating our options," Wenum said.

The DOW asks that people stay far from bighorns and all other wildlife during the winter months. Winter is a stressful time for wildlife as they live in a basic survival mode. Because of the cold weather and low availability of food, big game animals can lose 30 percent of their body weight during the winter. If approached by people, animals will move and be forced to burn extra calories that cannot be replenished. Expending extra energy will exhaust an animal and could cause it to die.

"If people want to watch wildlife during the winter, we ask that they use binoculars or a spotting scope and observe from a distance," Wenum said. "If animals move when they see you, you are too close."

Anyone who sees people harassing wildlife are asked to call a DOW office. The DOW office in Gunnison is (970)641-7060.